radioactivity

radioactivity /ra·dio·ac·tiv·i·ty/ (ra″de-o-ak-tiv´ĭ-te) emission of corpuscular or electromagnetic radiations consequent to nuclear disintegration; it is a natural property of all chemical elements of atomic number above 83 and and can be induced in all other known elements.radioac´tive

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artificial radioactivity , induced radioactivity that produced by bombarding an element with high-velocity particles.

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ra·di·o·ac·tiv·i·ty (rd--k-tv-t)

n.

1. Spontaneous emission of radiation, either directly from unstable atomic nuclei or as a consequence of a nuclear reaction.

2. The radiation, including alpha particles, nucleons, electrons, and gamma rays, emitted by a radioactive substance.

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radioactivity

[-activ′itē]

the emission of alpha or beta particles or gamma radiation as a consequence of nuclear disintegration. Natural radioactivity is a property exhibited by all chemical elements with an atomic number greater than 83; artificial or induced radioactivity is created through the bombardment of stable elements with subatomic particles or high levels of gamma radiation or x-radiation.

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radioactivity (rā´dēōaktiv´itē),

n spontaneous nuclear disintegration with emission of corpuscular or electromagnetic radiations. The principal types of radioactivity are alpha disintegration, beta decay (negatron emission, positron emission, and electron capture), and isometric transition. Double beta decay is another type of radioactivity that has been postulated, and spontaneous fission and the spontaneous transformations of mesons are sometimes considered to be types of radioactivity. To be considered radioactive, a process must have a measurable lifetime between approximately 1 and 10 seconds and 1017 years, according to present experimental techniques. Radiations emitted within a time too short for measurement are called
prompt; how-ever, prompt radiations, including gamma rays, characteristic roentgen rays, conversion and auger electrons, delayed neutrons, and annihilation radiation, are often associated with radioactive disintegrations because their emission may follow the primary radioactive process.

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radioactivity

the quality of emitting or the emission of particulate or electromagnetic radiation as a consequence of the decay of the nuclei of unstable elements, a property of all chemical elements of atomic number above 83, and possible of induction in all other known elements.

The chemical elements are made up of atoms, each of which consists of a nucleus around which orbits a cloud of negatively charged electrons. The nucleus itself is made up of two kinds of particles: neutrons, which have no electrical charge; and protons, each of which has a single positive charge. A neutral atom has an equal number of protons and electrons and no electric charge. The atomic number of an element is the number of protons in the nucleus of each of its atoms. The mass number of an element is the sum of the number of protons and neutrons in the nucleus.

All of the atoms of a particular element have the same atomic number, but can have different numbers of neutrons. An isotope of a chemical element consists of atoms having the same number of protons, but a different number of neutrons. When an atomic nucleus is unstable it decomposes or decays spontaneously, emitting high-energy particles. The emissions from radioactive decay can consist of electrons (beta particles), or electromagnetic energy in the form of photons, or helium ions (alpha particles). (See also radiation.) The process of decay can produce a product that is itself unstable, in which case it too will decay. The process continues until a stable nuclide is finally formed.

The radioactivity of a substance can be measured by determining the rate at which atoms decay in a given period of time. The basic unit of measurement of radioactivity is the becquerel (Bq), which is equal to 1 disintegration per second. The now outdated but possibly still used unit is the curie (Ci), which equals 37 thousand-million disintegrations per second. One-thousandth of a curie is a millicurie; one-millionth is a microcurie. These units of measure are used to calculate the dosage of radioactivity administered for various therapeutic procedures in much the same way that units of measure such as the gram and milligram are used to measure dosages of medications.

The half-life of an element is the time necessary for one-half of a given amount of the isotope to decay. Half-lives can range from thousands of millions of years to fractions of a second. The rate at which atomic decay occurs in a particular isotope cannot be altered by any outside force such as temperature, pressure or chemical reaction. The knowledge of the half-life of a particular isotope is essential to the proper handling of the substance for the protection of the medical staff and the animal receiving some form of radiation therapy.

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radioactivity

Radiation The spontaneous transformation of an unstable atom, often resulting in the emission of radiation and a lower energy state. See Airborne radioactivity, Radioactive decay.